Description of levels of evidence
| Evidence category | Sources of evidence | Definition |
| A | RCTsRich body of data | Evidence is from end-points of well-designed RCTs that provide a consistent pattern of findings in the population for which the recommendation is made. Evidence Category A requires substantial numbers of studies involving substantial numbers of participants. |
| B | RCTsLimited body of data | Evidence is from end-points of intervention studies that include only a limited number of patients, post hoc or subgroup analysis of RCTs, or meta-analysis of RCTs. In general, Evidence Category B pertains when few randomised trials exist, they are small in size, they were undertaken in a population that differs from the target population of the recommendation, or the results are somewhat inconsistent. |
| C | Nonrandomised trialsObservational studies | Evidence is from outcomes of uncontrolled or nonrandomised trials or from observational studies. |
| D | Panel consensus judgment | This Evidence Category is used only in cases where the provision of some guidance was deemed valuable but the clinical literature addressing the subject was insufficient to justify placement in one of the other categories. The Panel Consensus is based on clinical experience or knowledge that does not meet the aforementioned criteria. |
RCT: randomised controlled trial.